Driving mechanism



0. AKERMAN m- AL Aug. 27, 1957 DRIVING MECHANISM 3 Sheets-Sheet 1 Filed July 12. 954

I r I NVENTQRS.

Aug. 27, 1957 o. AKERMAN ETAL 2,803,975

DRIVING MECHANISM Filed July 12, 1954 I5 Sheets-Sheet 2 n min n n max n max INVENIORS. oznfim g- 27, 1957 Y o. AKERMAN ET AL 2,803,975

DRIVING MECHANISM Filed July 12, 1954 I 3 Sheets-Sheet 3 3 a 'lnv'entors;

United States Patent DRIVING MECHANISM Olov Akerman and Lars 010v Akerman, Stockholm, Sweden Application July 12, 1954, Serial No. 442,638

11 Claims. c1. 74-686) The present application is a continuation-in-part of our prior patent application Ser. No. 238,832, filed on July 27, 1951.

This invention relates to a driving mechanism comprising a primary driving motor and an electro-mechanical transmission unit allowing continuous change of speed and torque in both directions of power between the driving motor and the output shaft of the driving mechanism.

The electro-mechanical transmission unit employed in this connection is of the type including a planetary gear unit with a sun gear, a ring gear and a planet gear carrier with planet gears, of which elements the one is mechanically coupled to the shaft of the driving motor, the second to the output shaft of the driving mechanism and the third to an electric direct current motor-generator whose armature is electrically connected with the armature of another, similar direct current motor-generator which is mechanically coupled to either the shaft of the driving motor or the said output shaft, the one direct current motor-generator having a constant separately excitated magnetic field and the other a separately excitated mag netic field which may be altered in respect not only of its size, but also of its direction.

The objects of the invention will appear from the following text, where reference is had to the appended drawings, wherein Fig. 1 shows diagrammatically a driving mechanism according to the invention, while Fig. 2 shows a curve representing the speed ratio between the shaft of the driving motor and the output shaft of the driving mechanism,

Fig. 3 shows a corresponding modified curve, and

Fig. 4 shows a similar curve for a driving mechanism according to Fig. 1 with the step-gear areas included.

Fig. 5 shows diagrammatically a first modified arrangement of the driving mechanism compared with Fig. 1.

Fig. 6 shows diagrammatically a second modified arrangement of the driving mechanism compared with Figs. 1 and 5.

Fig. 7 shows diagrammatically a third modified arrangement of the driving mechanism compared with Figs. 1 and 5-6. a

Fig. 8 shows diagrammatically a fourth modified arrangement of the driving mechanism compared'with Figs. 1 and 5-7. a

Fig. 9 shows diagrammatically a fifth modified arrangement of the driving mechanism compared with Figs. 1 and Fig. 10 shows diagrammatically a sixth modified arrangement of the driving mechanism compared with Figs. 1 and 5-9. a

Fig. 11 shows diagrammatically a modified arrangement of the field windingsof the second motor-generator compared with Fig. 1.

Our invention relates to a combination in which are included the devices for purely mechanical transmission of power in automobiles,motor vehicles, locomotives etc., and devices which are generally applied for purely elec- 2,803,975 Patented Aug. 27, 1957 ICC tn'cal transmission by means of two direct current units, e. g. in diesel-electric locomotives. The adjustment of the torque and speed of the driven shaft is elfected in the former case by changing the fuel-feed and by the manipulation of step-gears, and in the latter case by adjusting the excitation of the direct current units, whereby the direct current unit connected with the driven shaft receives a varying voltage.

The main object of our invention is, with a certain set working program, to be able arbitrarily to reduce the size of the two direct current units and in spite of this to have the same working properties as with a pure electric transmission. This implies that hitherto unexpected possibilities for the application of continuous change of speed and torque are provided, since the electrical units can be made light, unbulky and cheap. At the same time the electrical transmission losses are reduced, which means increased efiiciency approaching the efficiency of the purely mechanical gear.

The adjustment of the speed of the driven shaft can according to ourinvention be made continuously from zero to any desired maximum speed m max according to the working diagram, Fig. 4. In this exemplified case the size of the electrical units is only 4, of that unit size which would be required for pure electrical transmission. The diagram Fig. 4 shows the speed n of the driven shaft as a function of the speed it of the driving motor. Thus within the interval n minrz max it is possible continuously to adjust the speed of the driven shaft without the speed it of the driving shaft being altered. If the driving motor is a combustion engine it will thus be possible with a constant fuel-supply to utilize also a constant effect W at all speeds of the driven shaft within the above-mentioned interval.

The combination does not, however, allow flux of power only in the direction from the driving unit to the driven shaft, but also in the reverse direction. Thus when the invention is applied in an automobile the kinetic energy of the automobile can be returned to the combustion engine, when a braking eifect is desired. Then the combustion engine works as a compressor without. supply of fuel and the Working properties will be those shown in Fig. 4, though the working direction is reversed.

The electrical transmission is the only known method in engineering practice which allows of adjustment of torque and speed in both directions of power with unchanged speed for the driving unit. The electrical transmission thus occupies a central position in modern engineering, but its general application is restricted by the fact that it requires heavy direct current units whose weights and dimensions increase with the ratio n max n min i The combination invented by us allows also of the continuous adjustment of torque and speed in both directions of power with unchanged speed for the driving unit, but allows of an arbitrary reduction of theweight and size of the electric units and thus also of their electrical losses as compared with those of the pure electric transmission. With our gear the practical possibility of exploiting continuous adjustment of torque and speed therefore assumes a new and more favorable position.

Referring now to Fig. 1, the reference-numeral 1 designates a combustion engine whose speed may be regulated by changing the fuel-supply by means of the two valves 2 and 3. Valve 2 is operated with a pedal 4 in the normal way, a maximum flow of fuel through valve 2 being effected in the wide open position of the pedal. When the pedal is released the fuel-supply is reduced to the point at which the combustion engine will be working at idling speed. Valve 3 is governed by a centrifugal regulator 5 which is mechanically coupled to the shaft of the combustion engine and controlled by the spring 6 with the operating handle 7. At a certain position of the operating handle 7 the centrifugal regulator 5 closes valve 3, when a speed of the combustion engine corresponding to the position set has been reached. When the engine speed falls below this value by a certain permitted margin, valve 3 opens. Due to this device the driver is never able with pedal 4 to obtain a higher speed for the combustion engine than that corresponding to the setting of the operating handle 7. The operating arm 3 connected with valve 3 closes, in the vicinity of its two end-positions, the two electric contacts 8 or 9 respectively, whose functions are described below,

The combustion engine 1 is connected, via the driving shaft 10, with the sun gear 11 of a planetary gear unit whose two other elements are the planet gear carrier 12 and the ring gear 13. Of these latter, the planet gear carrier 12 is connected, via the shaft 14, with the one half of a clutch 15, whose other half, via the shaft 16, is connected to a normal gear box 17, which, in the example, engages a step gear when the operating lever 18 is pushed over to the left and which efiects direct coupling when the operating lever is pushed to the right. The output shaft 19 from the gear box is in fact also the output shaft of the complete driving mechanism and may for example be connected to the rear axle of an automobile. By means of the clutch the intermediate shafts l4 and 16 respectively are disengaged when an auxiliary supply voltage is transmitted to an operating coil 20, which via the lever-arm 15 acts upon the clutch, whereby the contact 21 on the extension of the lever-arm 15 is closed. The changing of gear in the gear-box 17 is performed by means of two operating coils 22 and 23. When auxiliary supply voltage is transmitted to the operating coil 22 the step gear is engaged and remains thereafter in this position until supply voltage is instead transmitted to the operating coil 23, whereby the gear is changed into direct drive. The adjustment range obtained when the step gear is engaged is in the following designated range I, and the adjustment range obtained with direct coupling, range II. The ring gear 13 in the planetary gear unit is mechanically coupled to an electric direct current motor-generator 24, called the reaction unit, which is provided with a separately excitated field-winding 25. The driving shaft N is connected, via a gear transmission 26, to another direct current motor-generator 27 which is provided with a series winding 28 and a separately ex-citated field winding 29. The armatures of the two direct current units 24 and 27 are electrically connected with each other through a regulating resistance 39. Current for separate excitation of the fields of the direct current units, and for operating purposes, is taken from the battery 31. The separately excitated winding of the reaction unit 24 is connected with the battery over a settable resistance 32. The magnetic field (p generated by means of the winding 25 has therefore normally constant magnitude and direction. The magnetic field t generated by means of the field winding 29 in unit 27 can be adjusted from a maximum value in the one direction to the same maximum value in the opposite direction by means of the regulating device A, which is mechanically coupled to the booster unit B.

The regulating device A consists of a contact arm 33 which effects the adjustment of the magnetic field 5 in unit 27 on being moved over the annular resistance 34. with appertaining contact races 35 and 36. In the position shown in Fig. l the contact arm 33 is assumed to have moved cr in a clockwise direction from a starting position at the point a, where the contact arm 33 produces maximum positive potential. Operating current flows from the plus-pole of the battery to the point a on the resistance 34 and thereafter through both branches of the resistance to the point b, which is connected with the minus-pole of the battery. The resistance 34 functions in this connection as a potentiometer with zero-voltage in the two middle points c and d, which are both electrically connected with the one terminal of the field winding 29 of unit 27. The other terminal of this field winding is connected with the contact track 36 and has, consequently, the same potential as the contact arm 33. When the contact arm 33 moves from the starting position at a in a clockwise direction towards the zero-point c, the voltage in the field winding 29 will be reduced from a maximum value in the one direction to zero in point 0 and thereafter the said voltage will again successively increase but with reversed potential when the contact arm continues its movement to attain its maximum value in the reverse direction in the point b, wherein the contact arm has moved through 270. With continued movement of the contact arm .33 the voltage is again reduced to zero in the point d, to attain once more its original starting value in the point a after having thus moved through 360. The same process may then be repeated. On reversing the direction of rotation of the contact arm 33, all the phases of the process occur in the reverse order.

The booster unit B for the contact arm 33 consists of a piston 37 operated with pressure fluid, the direction of flow of which may be adjusted by means of the valve 38 through the agency of the electric valve operating coils 39 and 40. When voltage is transmitted to valve operating coil 39, valve 38 is switched over, so that the piston 37 moves, for stepping up, from left to right, and the valve maintains in this position until valve operating coil 40 gets current instead, when valve 38 is switched over so that the piston 37 moves in the reverse direction for stepping down. The value 38 is provided with a contact lever 41 which in the one end position closes a contact 41 in an operating circuit leading to the operating coil 23 and which in its opposite end position closes another contact 41" in an operating circuit leading to the operating coil 22. Auxiliary supply voltage to both these operating circuits is obtained only when the clutch 15 is disengaged and contact 21 at the clutch 15 is closed. Auxiliary supply voltage is transmitted to the valve operating coils 39 and 40 via the arm 3' on valve 3 when the latter closes on the contacts 8 or 9 respectively, the contact 8 closing the circuit through valve operating coil 39 and contact 9 closing the circuit through valve operating coil 40.

The connection between the booster unit B and the regulating device A consist of a rack 42 coupled to the piston 37 and a gear-wheel 43 which drives the contact arm 33. The diameter of the gear wheel 43 in relation to the length of the rack 42 is so chosen that one full stroke of the piston from left to right corresponds to an angular movement of the contact arm 33 over an angle of 360+270=630.

The above-mentioned rack 42 is provided with a contact arm 42' which within the interval 270-360 connects the positive pole of the battery with the operating coil 20 of the clutch 15 and also with the upper pole of contact 21. The current to the operating coil 20 passes a push-button 44. The function of this button is to enable a disengaging of the clutch while warming up the combustion engine with the car at a standstill without in this connection shifting gears, the button being kept pushed down until the engine is warmed up.

The resistance 30 cut in between the armatures of the direct current units is automatically and progressively short-circuited by means of the regulating device C, which consists of a contact arm 45 that during the starting period stepwise short-circuits this resistance in proportion as the armature tension in the direct current unit 27 rises. This function is effected by a magnetic coil 46 and a spring 47 counteracting the magnetic coil. During the first part of the starting period, the regulating device A is in its starting position with the contact 9 at the motor 1 closed, and the piston 37 is thereby pressed by the pressure-fluid through the valve 38 towards its left end position, a head 48 fitted to the contact-arm 42' then keeping a second short-circuiting contact device 49 for the resistance 30 broken.

The annular resistance 34 is adapted to supply a maximum potential to the field winding 2Q of the motorgenerator 27 that causes a magnetic field in that unit during the starting period which induces an armature voltage in unit 27 which is lower than the armature voltage induced in the reaction unit 24, so that the reaction unit 24 will work as a generator during the said start ing period.

Through the contact 50 the supply of current to the auxiliary circuits can be cut oif, e. g. in combination with the switch-key when parking the vehicle.

That the arrangement according to Fig. 1 gives the regulating result has been shown on the above-mentioned diagram 4 and calls for a closer study ofthe different working phases, so that the mode of functioning may appear clearly.

It is known that a planetary gear unit of the kind shown in Fig. 1 has the same properties as a normal toothed wheel gearing if one of the three elements included, e. g. the ring gear, is kept firmly braked while the other two are connected to the input and the output shafts respectively. The magnitude k of the gear ratio is here determined by the radii of the sun gear and the planet gears, and the speed of the output shaft will be n =n/k, where n is the speed of the input shaft. The torque absorbed by the firmly braked ring gear is in this connection a reaction torque that does not take any active part in the working process and does not give any eifect either.

In a planetary gear unit working in this way there is a constant relation between all the torques, because the tooth pressures acting upon each of the planet gears always balance each other. The consequence of this is also that all the torques of the elements within the planetary gear unit must change direction simultaneously with the flux of power when the directions of rotation of the input and output shafts are unchanged.

Further it will appear that the flux of power from the driving shaft to the driven shaft of the planetary gear unit is always combined with a flux of power through the reaction unit 24 and the unit 27 electrically connected thereto. The reaction torque which is hereby received or delivered by the reaction unit 24 is, if the value of the magnetization is unchanged, directly proportional to the armature current i, the direction and amplitude of which may be adjusted by changing the excitation ta in the unit 27. By controlling the reactive flux of power, the useful power flowing from the driving shaft 10 to the driven shaft 14 may thus be adjusted to any desirable value. Since no reactive power departs from the systemif the losses in the units 24 and 27 and in the resistance 39 switched in during the first starting period are neglected--the power taken up by the driven shaft 14 will be equal to the power supplied by the driving shaft 10, which physically means that conversion of speed and torque is obtained.

If according to the example in Fig. 1 reaction torque is absorbed or created by means of the reaction unit 24, continuous electro-mechanical gear having the same properties as a normal toothed wheel gearing is obtained with the transformation k when the reaction unit is at a standstill, but which for every positive or negative speed of the reaction unit shows another gear ratio.

If the speed of the sun gear 11 is n, that of the planet gear carrier 12 is n and that of the ring gear 13 is u every such gear ratio is determined by the formula:

ra -n,

This formula may also be written thus:

n =n in,

where n,,(:n/ k) is the speed of the output shaft with the ring gear at a standstill, in the following designated medium speed, and

is a relative speed to n depending on the speed and direction of u i. e. on the speed and direction of rotation of the ring gear.

In the example according to Fig. l the medium speed n of the outgoing shaft 14 may be adjusted by altering the supply of fuel to the combustion engine 1 by means of the pedal l. The adjusting of the relative speed n is effected by field regulation, the excitation 5,, of the direct current unit 27 being adjusted by means of the regulating device A with appertaining booster unit B, whereby the armature-voltage of this unit is changed from a positive to a negative maximum value or vice versa. Since the reaction-unit 24 works with a constant magnetization o this unit will work, when under the influence of the abovementioned armature-voltage, with varying speed u from a maximum value in the one direction of rotation to the same maximum value in the other direction of rotation, which, according to what has been said above, means that the gear ratio between the shafts 10 and 14 will be continuously altered from the one extreme limit to the other. At a certain speed n of the combustion engine, the speed 11,, of the shaft 14 is thus varied from n n to 11 4-21, or vice versa.

With the arrangement according to Fig. 1 it is possible to change at will not only the speed-components n and 11,, but also the magnitude and direction of the reaction torque, which is precisely determined by the product of the armature current i through the reaction unit and the field (p of said unit. If is constant, the torque is thus exclusively determined by the magnitude and direc tion of the armature current i, which in its turn depends on the field-potential set for the direct current unit 27. A reversing of the direction of current between the units 24 and 27 means that all the torques in. the planetary gear unit, as has been pointed out before, are reversed, and therewith also the flux of power.

If the arrangement according to Fig. 1 is to function correctly, it is necessary that the direction of torque of shaft 14 should be unchanged as long as fuel is being supplied to the combustion engine, but be reversed when the supply of fuel is cut oif, whereby braking is effected.

We have found that in our system the reaction unit 24 does actually, in its Zero passage (n =0), maintain its direction of torque unchanged, i. e. passes from generator-running to motor-running or vice versa. With every other transmission known to us, where an electric unit is in this way caused to change from the one direction of rotation to the other exclusively by a reversing of the armature voltage supplied, also its direction of torque is always reversed at this zero-passage. Our invention therefore gives in this respect an unexpected and surprising effect, which is due to the interplay between the electrical power flux in the direct current units and the mechanical power flux in the planetary gear unit, which has also been confirmed by tests with various units of the kind herein described.

In normal automobile operation with step-gears the speed of the driven shaft can be continuously regulated only by adjusting the speed of the engine by means of the throttle, whereby the well-known saw-toothed speed and eifect diagrams are obtained. In using pure electrical transmissions all changes in the speed of the driven shaft are made electrically. The electro-mechanical gear according to the invention illustrated in Fig. 1 thus constitutes a combination of these two transmission principles, as the speed n of the shaft 14 from the planetarygear unit depends both on the medium speed n and the relative speed n where according to the example the magnitude of n is regulated by means of the pedal 4, while the magnitude of 11 is regulated electrically by means of the regulating device A with the booster unit B. The developed technique, upon which e. g. the automobile industry is based, is therefore utilized in our transmission together with the technique based upon the pure electrical process.

Whereas with n no flux of electric power occurs in our transmission, and the whole flux of power is, consequently, purely mechanical, the electric reaction power rises, with unchanged reaction torque by the relative speed 11 to reach its maximum when the reaction unit is running at full speed. If in this connection the relative speed n is so-great and has such a direction that n ,,,:0, i. e. that the shaft 14 is at a standstill, the mechanical power transmitted to this shaft must instead be equal to zero and the electrical component through the reaction unit 24 will consequently, if the losses are neglected, be just as great as the output power from the combustion engine. if this reactive power is returned, according to the example in Pig. 1, via unit 27 to the shaft 10 of the planetary gear unit, the combustion engine will be relieved and consequently it will give no active power despite the fact that full torque is obtained on shaft 14, or in other words a closed circle of power-transmission is obtained where the power flux is partly mechanical, through the planetary gear unit, and partly electrical, through the units 24 and 27.

if, now, instead, according to Fig. 5, unit 27 is connected to the shaft 34, the reaction power during the first starting period can only be partly absorbed by this unit before it has attained a suificient speed. In the same way as is often applied with pure electrical regulation it is possible to overcome this difiiculty with an adjustable resistance in the armature circuit between the two direct current units, which absorbs the difference in power and which can be short-circuited as soon as shaft 14 has reached such a high speed that unit 27 is able itself to receive the entire reaction power.

The method of returning the reaction power to the driving shaft has therefore a certain advantage during the first starting period from standstill. Also with this latter method according to Fig. 1, however, a corresponding resistance 3h cannot be entirely avoided, as the speed n is changed and therewith also the speed of the unit 27. In both the alternatives the reactive power can be totally or partly utilized as soon as the unit 27 has reached a sutlicient speed, and the electric wiring plan is the same for both alternatives, which thus also means that in both cases the speed-components I1 and n can be individually regulated.

if the arrangement were so ordered that at the start from standstill the relative speed n, where just as great as the medium speed 21. with full speed it of the combustion engine 1, and consequently the reaction unit 2 5- would be able to absorb the full reaction torque at the speed that it would then be given by the ring gear 13, the reaction unit 24 would need to be dimensioned for the same maximum flux of power as corresponding units in the pure electrical process, and no technical development would consequently be attained hereby. If, however, when the medium speed n has been reached, the relative speed 11 can also be regulated to a maximum in the r verse direction, the total extent of the working range will of course be doubled, or 2:1 which in its turn means that with the same extent of working range the direct current units will be half the size of those needed with pure electrical regulation. Considerable gain in respect of the sizes of the units must here be weighed against the complication entailed by the planetary gear unit. 1

We have realized that a revolutionizing change as regards continuous transformation of speed and torque is not possible unless the electric units required can be further radically reduced. In this connection we have found that the desired goal can be attained if according to the example in Fig. 1 adjustment of both the com ponents n and n is employed. 7

With automobiles a start in the first gear-position is had by continuously increasing the speed of the combustion engine from a certain minimum idling speed to a predetermined maximum speed. This start, however, can only be carried out if a friction-clutch or the like is installed between the combustion engine and the driven shaft to absorb, at the moment of starting, the difference in the power supplied by the combustion engine and received by the driven shaft. This part of the starting interval during which the friction-clutch is used is an unavoidable consequence of the fact that starting must take place when the engine works at an idling speed, and it contributes to reduce the effectiveness and safety of the start, makes the operation more difficult and necessitates an uneconomical over-dimensioning of the gear-ratio at the start.

if when using our transmission according to the embodiment exemplified in Figs. 1 and 5 the same possibility of regulating is utilized, i. e. by starting from a certain minimum idling speed n the relative speed :1 necessary for start from standstill is reduced in the same proportion as the idling speed and therewith also the reaction power. it is hereby possible to make a start without the use of a friction-clutch, as appears from Fig. 2, curve N1, which shows the speed n of the combustion engine as a function of the speed n of the shaft 54- from the planetary gear unit. With the combustion engine running at a speed of n also the corresponding n -value is reduced in the same proportion, and therewith also the na ative reiative speed --n, which required if a start is to be made from standstill of the shaft 14. According to the diagram Fig. 2, the relative speed maintains its value unchan cd when the speed of the combustion engine is increased from rz to 11 whereby the shaft 14 has attained the speed 11 min. From this value the speed of the shaft in can be further increased to n max with the speed of the cornbustion engine unchanged, since the relative speed is changed from its maximum value in a negative direction (-n to the same maximum value in a positive direction (l-m With a certain maximum value of n it is, as appears from Fig. 3, also possible to start from a lower idling speed than corresponds to the maximum value of n chosen. As in Figs. 2 and 3 the start is made with reduced speed of the combustion engine, the armature voltage in unit 27 will with full field also sink proportionally to the speed. If in these circumstances also the reaction power is to be absorbed, it is necessary, as mentioned earlier, to cut in a resistance 2E0 in series .with the armatures of the direct current units, according to the application shown in Fig. l, for the starting.

If with a fixed gear and friction clutch according to the normal principle in automobiles the same regulating range On,, max should be bridged over a dashed working line N2, Fig. 2, would be obtained whereby full output power could only be obtained at a single speed 11 max, since it is only at this point where the combustion engine Works with full speed. With our regulation according to the curve N1, Fig. 2, on the other hand, the con'ibustion engine has its full speed Within the whole working interval n minn max, so that also full output power may be utilized within the whole of this range, whose extent is 211 The curves N1 and N2 on the diagram, Fig. 2, may therefore also represent the maximum available effect (W). The sectioned surface in Fig. 2 represents in this connection the minimum energy that must be absorbed by the friction clutch when starting according to normal automobile-principle, which consumption of energy is thus avoided when starting with our gear.

If, instead of this, the same working interval is to be bridged over with pure electrical regulation, the electrical direct current units must be dimensioned for the whole of the speed-interval -n max. The relation between the relative speed it, and the maximum speed n max is therefore an expression for the unit sizes in our transmission as compared with pure electrical regulation. With the reduced electric power flux in our process, the electrical losses sink in a corresponding degree, resulting in a higher efficiency. Also in this respect our transmission occupies an intermediate position between the pure toothed wheel gearing and the pure electrical system of transmission and approaches the properties of the mechanical toothed wheel gearing in this respect in the degree in which the relation between n, and n max can be reduced.

From Figs. 2 and 3 it appears that the less the relative speed n and therewith the electrical power-component, the less also will be the interval n min-it max within which full output power is available. This limitation can, however, be avoided by the introduction of a step-gear unit 17, according to the example shown in Fig. 1, interconnected between the shaft 14 from the planetary gear unit and the output shaft 19, which may be disengaged by means of the clutch 15. Herewith the well-tried methods applying in automobile operation have thus been further taken advantage of in the continuous regulating process according to our principles.

Whereas in an automobile such a step-gear unit always entails discontinuities in the speed of the combustion engine when changing gear, in the combination described by us it is possible to maintain the continuity and a change of the step-gear may consequently take place Without any change in the speed of either the driving or the driven shafts and 19 respectively. The prerequisite for this is that the ratio between each subsequent step in the gear-unit should be u=n max/n, min, where n max and n min are the indicated limits in Figs. 2 and 3.

If we assume, to begin with, that the step-gear unit 17 consists only of one gear-stage with this transformation it, which is interconnected within range I in Fig. 4, after which the change of gear is made to direct coupling within range II, the working conditions will be the following:

When starting with idling combustion engine the speed n of the output shaft 19 will in this connection show a course corresponding to that in Fig. 2 or in Fig. 3. When the maximum speed within the range I has been attained, the step-gear is disengaged in the way indicated in the exemplified application. If at the same time as this disengagement is effected the relative speed is switched from +12, to n in the manner also shown in the exemplified case in Fig. l, the resulting gear ratio will when the clutch is again thrown in remain unchanged on entering the range II, because the gear ratio in the planetary gear unit has hereby been increased just as much as it has been reduced in the step-gear unit through the direct coupling.

On entrance to the range II.the total reduction of gear is thus unchanged, but the medium speed has on account of the disengaged step-gear risen from n to 14.11 For the same reason, the relative speed, referred to the shaft 19, has become u'.n,. By renewed regulation of n, from its maximum value in the one direction to its maximum value in the opposite direction the speed of the output shaft 19 within the range 11 will increase to m max=u .n min. In the diagrams in Figs.

2-4 is u==3, and consequently in Fig. 4 is n max=9n min. Through the combination of the planetary gear unit and its electrical units with the step-gear it has been possible to reduce the relative speed n, to of the total regulating range, which also means that the electrical units in our transmission will only be ,4, the size of corresponding units with pure electrical regulation.

Even with the application of one step-gear according to Fig. l and Fig. 4 a regulating range that well covers most practical requirements is obtained. For an ordinary automobile with a step-gear unit having several stages the highest speed at which full effect is available is as a rule only about 3-4 times higher than the lowest possible speed with full effect, thus less than half as great as in the example. There is, however, nothing to prevent a further increase of the regulating range according to the same principle, whereby in the exemplified application the range of regulation is tripled for every further gear stage added.

Since herewith both the mode of working of the single details in Figs. 1 and 5 and the basic principles upon which our transmission is founded have been explained, it is now possible to describe the mode of functioning in its entirety, it being assumed that the appliance is installed in an automobile:

Before the automobile is started the contact 50 is closed, e. g. by means of the switch-key, whereby battery-voltage is transmitted to the magnetization and auxiliary circuits. As the combustion engine is at a standstill the centrifugal regulator 5 keeps contact 9 closed whereby the coil 40 gets voltage and the pressurefluid from a suitable source i. e. a motor driven oil-pump not shown in the diagram pushes the piston 37 in the booster unit B towards its left end position, so that the contact 49 is kept broken at the same time as the contact arm 33 is held in its starting position. At the same time the field winding 25 on the reaction unit 24 gets current via the settable resistance 32 and the magnetic flux 3,, is built up, while the field winding 29 of the direct current unit 27 via the regulating device A gets full field-potential in the one direction, so that the flux e is built up.

Now the combustion engine 1 is started to idling speed n whereby also the direct current units begin to rotate. If the magnetic coil 46 in the regulating unit C is so dimensioned and adjusted that at idling speed the contact-arm 45 is in its bottom position, the armature-current i through the direct current units is reduced to a minimum or broken and consequently practically no reaction torque is obtained in the reaction-unit 24. Accordingly, the combustion engine 1 rotates at no-load without any driving torque being transferred to the o11tput shaft 19. Thus in the diagram in Figure 4 is n =O and n=n With idling speed the operating lever 18 of the gear-box 17 always lies to the left and subsequent start therefore always takes place within the range I (see below).

When starting the automobile the pedal 4 is pushed down, whereupon the combustion engine begins to increase in speed and therewith also the voltage in unit 27. In consequence of this the operating arm 45 begins to move upwards and a current i begins to flow through the annatures of the direct current units, whereby a reaction torque is obtained in unit 24 and consequently also a driving torque in the output shaft 19, so that the automobile starts. In the degree in which the speed of the combustion engine and therewith the armature voltage in unit 27 rises, more and more of the resistance 30 is disconnected through the movement of the operating arm 45. The speed n. of the output shaft rises, in this connection, within the range 0--n min, at which latter speed the combustion engine has attained the speed set with the operating handle 7. As long as the handle 7 remains in this position the speed of the engine will never exceed the set maximum speed, e. g. 2000, 3000 or 4000 R. P. M.

As soon as the speed thus set has been attained, the centrifugal regulator 5 begins to function, whereby the 11 contact 9 is broken and the contact 8 closed instead. The coil 39 hereby gets voltage and the valve 38 opens for stepping up, whereupon the operating piston begins to move to the right and hereby brings the contact arm 33 clockwise from the starting position at a. At the same time the contact 49 is hereby closed, and any renianent resistance is short-circuited independently of the position in which the operating arm may be. From this moment the equipment thus works without any stray losses in the resistance 30.

When the contact arm 33 moves towards the point e the magnetization o sinks, and therewith the voltage of the direct current unit 27, from its maximum value in the negative direction to zero, and the speed of the reaction unit 24 then passes its zero-value. The speed n of the output shaft 19 has hereby increased from m min to n i. e. to its medium value with the step-gear in operation range I. With continued movement of the contact arm 33 towards the point b the flux in the unit 27 is increased in the direction opposite to the preceding one, and thereby the unit 27 begins to function as a generator While the reaction unit 24 takes over the motor-function. Both the direction of the armature current i and the direction of the torque remain unchanged. The speed n of the output shaft 19 rises further, herewith, from n to its maximum value n +n within the range I with the step-gear in operation.

At point b the contact arm 33 has moved 270 and the contact arm 42' begins to close the supply of operating current to the operating coil 20 of the clutch 15 so that disengagement is effected. On continued movement of the contact arm 33 from position b to position a the field potential in the direct current unit 27 is switched over from its positive maximum value to its negative maximum value and thus attains in the point matter movement of the contact arm 33 through 360, the same position as at the speed n =n min. Hereby also the reaction unit 24 reverses its direction of movement and attains, conse quently, also at point a the same starting state as at n =n min. This switch over within the range b-a tak s place with disengaged output shaft and consequently without any torque during the disengagement period being transmitted to the output shaft 19, which therefore substantially retains its speed n =n +n During this disengagement period operating current is switched on via contact 21 at the clutch 15 via the contact-arm 51 on the valve 38 to the operating coil 23 011 the gear-box 17, whereby the operating lever 13 is put over to the right and direct coupling is effected in the gear-box. On account of the selected ratio of gear u indicated in the foregoing, the speed of the input shatt 16 in the gear-box will herewith attain the same value, in point a, as the speed n of the shaft 14, i. e. there is synchronism and the clutch can be thrown in without any slipping worth mentioning occurring in the clutch 35. This takes place when the contact arm 33 passes the point a after an angular movement through 360.

On entering the range II the switch-over to direct gear has thus been made without requiring any change in the speed of either the driven or the driving shafts.

On continued movement of the contact arm 33 the same procedure as formerly within the range n i n takes place, but on account of the change of the gear 17 to direct coupling the new medium speed of the shaft 19 will within the range II be 11.21 and the new relative speed iiiJl When the contact arm 33 has moved through 360+270 the operating piston 37 has reached its right end position and the automobile has herewith attained the maximum speed available at the motor speed set by means of the operating handle 7 for the combustion engine, e. g. 80, 100 or 120 miles/h. The operating handle 7 can be moved for adjustment during driving r 12 both Within the range I and the range II, whereby according to the same principles as described above the start to the new speed takes place automatically, partly by adjusting the medium speed n and partly by adjusting the relative speed n in all operations the driver can with the pedal 4 adjust the acceleration to its maximum value with full fuel-inlet. If in this connection the speed of the combustion engine exceeds the set value, the fuel-regulator 5 closes in the manner described in the foregoing and it is consequently not possible for the driver to attain a higher maximum speed for the automobile than the speed set, e. g. miles hour, even if he pushes the pedal 4 to its wide open position. The driver thus has the possibility with the pedal 4- to change the acceleration at will up to the maximum speed set with the handle 7.

if the driver wishes to brake, he releases the pedal 4, whereby the combustion engine 1 will tend to lose speed, so that the operating arm on the valve 3 switches over to the contact 9, which results in the operating piston 37 beginning to move to the left towards the bottom position. In his connection also the contact arm 33 begins to work in the reverse direction. The automobile then returns its inertia to the combustion engine and maintains the speed thereof set with the operating handle 7. The process is here the same as in connection with the starting according to Fig. 4, but the speed of the automobile decreases from n max to zero, with automatic switch-over of gear from direct coupling to step-gear, when the boundary-zone between the ranges II and I is passed.

The same process takes place if the automobile is going uphill and the fuel-inlet 4 set by the driver is not sufficient to maintain the speed of the automobile on the ascent. The contact arm 33 moves, in this connection through such a large angle counter-clockwise, if necessary with automatic change of gear, that equilibrium in the ascent is obtained-at the position of the pedal 4 set by the driver. Since after the starting, the automobile must always be returned to standstill, the gear-stage will, with the given arrangement, always be in the range I when the automobile is stationary, and this independently of whether at braking also an auxiliary brake is used.

From the foregoing account it appears that the disconnecting period within the angle 270-360 or vice versa should be as short as possible. This can be attained by making this operating angle smaller and by increasing the speed of the contact arm 33 within this angle. Since during disengagement of the clutch only the armatures in the direct current units need to have their speeds changed, there is no practical obstacle to such a quick readjustment.

in order to render possible further increased starting torque we may, during the first part of the starting period, increase the flux 1% by adjustment of the resistance 32.. A large number of such possibilities exist for those who have studied the theoretical mode of functioning of our transmission with adjustment of medium speed and relative speed and change of gear.

In the example, the gear-box 17 is equipped only with one gear-stage and direct coupling. If several gear-stages are used consequently several working ranges in the diagram in Fig. 4 are obtained and the contact-arm 33 performs, in this connection, a movement with several revolutions and disengagement zones.

How the working operation according to Fig. l, especially at start, can be explained in relation to the diagrams in Figs. 2 and 3, e. g. when practicing the invention on a car, appears from the following exposition.

If when the car is at standstill the combustion engine works at idling R. P. M. and no exciting current is supplied to the two units 24 and 27, since the starting contact St is broken, unit 24 will run at a speed and with a direction of rotation such, that according to the basic equations in column 5, line 75 and column 6, lines 1 to 12, n,.=n n,=0, i. e. n =n,. In this connection the two units 24; and 27 will be idling, as they have no field excitation and consequently no armature current. Thus no reaction torque can be exercised by the reaction unit 24 and consequently no driving torque can be supplied to the output shaft 14.

When the starting contact 50 is closed, the two units get full field excitation (p and max respectively, as in this connection the device A is in its starting position (i. e. a=0). If the field excitation of unit 27 is here limited to a maximum value such that the voltage induced in unit 24 is higher than the voltage induced in unit 27, an armature current will begin to flow from unit 24, which in this connection works as a generator. This current is then supplied, via the resistance 30, to unit 27, which will here function as a motor. The magnitude of the current will depend upon the difference between the two induced voltages and upon the total ohmic resistance in the armature circuit, i. e. upon the internal resistance of the units and upon any existing external booster resistance 30, which may for the time being he assumed to be equal to zero.

Thus if the field qb is limited to a suitable intensity, any desired starting current i may be obtained, and there with any desired strength of the mechanical torque absorbed by the unit 24 functioning as generator, the socalled reaction torque, which is entirely determined by the product of irp (see column 6, lines 37 to 46, above),

i. e. by the armature current and field of the unit. From this it also follows, according to the above account, that the starting torque applied to the driven shaft 14 when the car is at stand-still may be set in advance through the limitation of the field max already referred to.

Since in the starting moment the car is standing still, however, this starting torque does not transmit any power to the driven shaft. It is thus at the starting moment necessary to supply only so much fuel to the combustion engine that its power compensates the mechanical and electrical losses arising in the rotating parts at the preset minimum starting current i mentioned before.

If now the fuel supply is increased above the said minimum value the speed of rotation of the combustion engine begins to rise and hence also the difference between the two voltages induced in the units 24 and 27 respectively. As a consequence hereof the before-mentioned current i will increase and so does also the torque on the driven shaft. The abovementioned preadjustment of the field o max is assumed to be carried out in such a man ner that at latest at the speed 11 the driven shaft 14 begins to accelerate from standstill, as illustrated in Figs. 2-4.

Thus while at the starting moment no useful power is communicated to the driven shaft, and consequently the starting torque may be high even with inconsiderable fuel supply, in connection with increasing speed ni of the driving shaft the power begins to increase with the useful power that hereby begins to be. communicated to the driven shaft 14. The fuel supply must thus be increased if the combustion engine is to be able to convey this increased power and further increase its speed. The time it tal ies for the car to attain the speed n min from standstill will consequently depend on how quickly the driver depresses his accelerator. With each increase of fuel supply the speed of the combustion engine will be increased only so much beyond the speed 11 that the useful power communicated to the driven shaft together with the losses arising will be equal to the power of the combustion engine in connection with this increased fuel supply. The only prerequisite is that at the starting moment the driver should supply at least so much fuel that the losses arising on account of the previously set starting torque for standstill can be made good by the combustion engine, which will otherwise stop.

.Thus with the limitation of the field excitation max of the unit 27, the speed of the combustion engine may be forced at the starting of the car to follow the rising part of the speed-curve N1 (see Figs. 2 and 3), provided only that the fuel supply exceeds a certain minimum value. With suflicient fuel. supply the maximum permitted speed of the combustion engine, n=n is attained, in which connection the starting time will be shortest it full fuel supply is used. As soon, however, as the speed of the combustion engine begins to exceed this highest permitted speed, the centrifugal regulator 5 starts to function and the field gb begins to diminish in response to the eifect of the device A, as described in detail above. The speed-curve N1 of the combustion engine will in this connection at n =n min merge from its previous ascent into the horizontal.

Since at n=n as follows from the above exposition, the current i flowing through the units 24 and 27 cannot be of greater intensity, and the torque of the driven shaft 14 caused by this current at the speed n min does not communicate to the driven shaft more power than corresponds to that emitted by the combustion engine, the voltagesinduced in the units cannot in this point differ more from each other than corresponds to the units internal ohmic voltage drop. This internal voltage drop is in normal electrical units at full load of the order of magnitude 10% of the induced voltage, thus for two units connected in series about 20%. The less the induced voltage in the unit 27 is, the less, consequently, will also be the corresponding induced voltage in unit 24, and therewith also the relative speed -n If a relatively low value of this relative speed n, should be desired, in order therewith to get a low power of the electrical units 24 and 27, it may be necessary to limit max to a lower value than corresponds to the setting of the maximum torque for the first starting moment, which maximum torque would hereby come to be greater than what is required for the starting of the car. If, however, no increase of the maximum torque is desired in the starting moment, the starting torque required for the starting of the car may nevertheless also in this case be retained, if a booster resistance 30 is introduced in series with the armatures of the units as shown in Fig. 1, which resistance, as emerges from the description in the foregoing, is automatically short-circuited by the device C when the speed of the combustion engine increases from its lowest value n Through these measures the fundamental principles on which the working diagrams in Figs. 2-4 are based may be applied in practical operation, whereby, as has been shown in detail in the above exposition, one obtains a very important development of the electro-mechanical gear, as it can be executed with considerably smaller electrical units than is otherwise possible.

In the application exemplified it is assumed that the driving motor is a combustion engine. Our transmission may, however, be connected, with unchanged principles, to any driving motor or driving unit, the speed of the driving shaft of which can be adjusted for the attainment of different values of the medium speed.

The basic equation for the speed relations between it, n and u given in the foregoing applies unchanged if the reaction unit 24 is connected to another of the three elements included in the planetary gear unit than the ring gear, e. g. to the sun gear, the two other elements being connected to the driven and the driving shafts respectively. The principle of medium speed and relative speed remains, also with such other combinations.

In Figs. 1 and 5 the driving shaft 10 is coupled to the sun gear 11 and the driven shaft 14 to the planet gear carrier 12, which combination, as herein before described,

gives a medium speed of the driven shaft which is k times the speed of the driving shaft.

In Fig. 6 the driving shaft 10 is coupled to the sun gear 11 and the driven shaft 14 to the ring gear 13, which combination gives a medium speed of the driven shaft which is 13. With a gear ratio between the shaft 14 and the ring I gear 13 amounting to 1:1 the medium speed of the driven shaft 14 will be times the speed of the driving shaft.

In Fig. 9 the driving shaft 10 is coupled to the ring gear 13 and the driven shaft 14 to the sun gear 11, which combination gives a medium speed of the driven shaft which is l-k times the speed of the driving shaft.

In Fig. 10, finally, the driving shaft 10 is coupled to the ring gear 13 and the driven shaft 14 to the planet gear carrier 12. With the gear ratio 1:1 between the shaft 14 and the planet gear carrier 12, this combination gives a medium speed of the driven shaft which is times the speed of the driving shaft.

All these combinations according to Figs. 1 and 5 and 6-10 therefore give different values on the medium speed of the driven shaft at a certain constant speed of the driving shaft and at a certain ratio between the radii of the sun gear and the planet gear, i. e. at a certain k-value. The most favourable combination depends upon the medium speed desired on the driven shaft at a certain speed of the driving shaft.

The difference between Fig. 5 and Fig. 1 is, that in Fig. 5 the unit 27 has instead been coupled to the driven shaft 14, which, however, does not alter the medium speed of the driven shaft. In the same way it is possible, in Figs. 6-10, to couple the unit 27 to the driven shaft instead of to the driving shaft.

The direct current unit 27 can, as in example in Fig. 1, be provided with a series winding 28 the function of which is to stabilize the circuit, according to the same principles as are normally applied to separately excitated direct current units. This winding is connected in such a way that the armature-voltage of the unit sinks, when the machine is working as a generator, if the current in creases, i. e. so that it counteracts shocks due to load.

In all other known cases where the flux of a direct current unit is adjusted so that the armature-voltage is changed from a positive to a negative value or vice versa, such a series winding always means that stability is attained, certainly, at the one polarity of the armaturevoltage but not at the other, in which instead increased instability is obtained, while hereby the direction of cur rent flow is reversed.

In the combination given by us in Fig. 1, on the other hand, the series winding will have a stabilizing effect in both the polarities, because as shown earlier on reversal of the polarity of the armature-voltage the unit always passes from generator-running to motor-running or vice versa, i. e. maintains the direction of current flow unaltered. Such a series winding is of particular importance where the change of speed is desired with constant or slightly changeable torque, as is often the case with working units of difierent kinds. The damping effect of the series winding can,

'as shown on Fig. 11, be strengthened by providing the unit 27 with a field-winding 51 with the adjusting resistance 52, which is fed with the armature-voltage of the unit and which strengthens the separately excitated field-winding .29 when the unit is functioning as a generator. Also in this case the damping remains unchanged at both thevoltage-polarities, whereas in all other processes known to us, this combination only gives the desired result at the one voltagepolarity.

In this respect, too, our transmission thus gives an effect not earlier known, which allows of valuable possibilities of regulation. No change arises if the direct current unit 24 is instead provided with the series winding mentioned or with a combination of series winding and self-excitated field-winding. Also in this case the windings are to act damping when the unit functions as a generator.

We have herein described the principle of our invention and illustrated a preferred embodiment thereof. Various modifications will occur to those skilled in the art and we desire it to be understood that all modifications which fall within the terms of the appended claims are to be considered as falling within the scope of our invention.

We claim:

1. In a driving mechanism the combination of a driving unit having a driving shaft, accelerator means for increasing the speed of said driving shaft from a lower starting speed to a working speed considerably higher than said starting speed, means for maximizing the said working speed of said driving shaft at a preselected value, a planetary gear unit including a ring gear, a sun gear and a planet gear carrier having planet gears each in mesh with both said ring gear and said sun gear, one of said elements of said planetary gear unit being coupled to said driving shaft of said driving unit, an output shaft of the mechanism coupled to a second one of said elements of said planetary gear unit, a first direct-current motor-generator coupled to the third one of said elements of said planetary gear unit, which, when rotating in one direction, causes an increase of the speed of said output shaft relatively to a medium speed thereof obtained when said first motor-generator and its related planet gear unit element is at standstill, and, when rotating in opposite direction, causes a decrease of the speed of said output shaft relatively to said medium speed, a separate field excitation equipment for said first motorgenerator, a second direct-current motor-generator coupled to one of said planetary gear unit elements other than that coupled to said first motor-generator, said two motor-generators having their armatures electrically connected in series, a separate field excitation equipment for said second motor-generator including control means for adjusting and reversing the separately excitated field of said second motor-generator, and means for keeping said control means in a position assuring such a field excitation in said second motor-generator during the acceleration of said output shaft from standstill to said medium Working speed, that the armature voltage induced in said second motor-generator is lower than but has a polarity opposite to the armature voltage induced in said first motor-generator even at standstill of the output shaft, and sothat the relative speed, caused by said first motor-generator, is arbitrarily lower than said medium speed when the driving unit works at its full working speed.

2. In a driving mechanism the combination as claimed in claim 1, wherein said second motor generator is coupled to that planet gear unit element which is coupled to said driving shaft of said driving unit.

3. In a driving mechanism the combination as claimed in claim 1, wherein an electrical resistance is interconnected in series between said armatures of said two motor-generators, and wherein means are provided for short-circuiting said resistance at least as soon as said teas rs 17 drivingshaft of said driving unit reaches its predetermined maximum speed.

4. In a driving mechanism the combination as claimed in claim 1, wherein said driving unit includes a combustion engine, a speed regulator for said engine determining themaximum working speed thereof, and throttle means for varyingthe speed of said engine between a lower, idling speed and said maximum working speed, the operation of said control means for adjusting and reversing the separately excitated field of said second motor-generator being dependent on the speed of said engine and hence of the operation of said throttle.

5. In a driving mechanism the combination as claimed in claim 1 wherein booster means are provided for actuating said control means for adjusting and reversing the separately excitated field of said second motor-generator, and wherein means sensitive to the speed of said driving shaft of said driving unit are provided for controlling the operation of said booster means.

6. In a driving mechanism the combination of a driving uni-t having a driving shaft, accelerator means for increasing the speed of said driving shaft from a lower starting speed to a working speed considerably higher than said starting speed, means for maximizing the said Working speed of said driving shaft at a preselected value, a planetary gear unit including a ring gear, a sun gear and a planet gear carrier having planet gears each in mesh with both said ring gear and said sun gear, one of said elements of said planetary gear unit being coupled to said driving shaft of said driving unit, an output shaft of the mechanism coupled to a second one of said elements of said planetary gear unit, a first direct-current motor-generator coupled to the third one of said elements of said planetary gear unit, which, when rotating in one direction, causes an increase of the speed of said output shaft relatively to a medium speed thereof obtained when said first motor-generator and its related planetary gear unit element is at standstill, and, when rotating in opposite direction, causes a decrease of the speed of said output shaft relatively to said medium speed, a separate field excitation equipment for said first motor-generator, a second direct-current motor-generator coupled to one of said planetary gear unit elements other than that coupled to said first motor-generator, said two motor-generators having their armatures electrically connected in series, a separate field excitation equipment for said second motor-generator including control means for adjusting and reversing the separately excitated field of said second motor-generator, means for keeping said control means in a position assuring such a field excitation in said second motor-generator during the acceleration of said output shaft from standstill to said medium working speed, that the armature voltage induced in said second motor-generator is lower than but has a polarity opposite to the armature voltage induced in said first motorgenerator even at standstill of the output shaft, and so that the relative speed, caused by said first motor-generator, is arbitrarily lower than said medium speed when the driving unit works at its full speed, a step gear box interconnected between said output shaft of the mechanism and that planetary gear unit element coupled to said output shaft, a clutch between said gear box and said last-mentioned planetary gear unit element, means for operating said clutch and means for shifting gear in said gear box.

7. In a driving mechanism the combination as claimed in claim 6, wherein means are provided for automatically disengaging the cluch, shifting gear and reengaging the clutch and for simultaneously reversing the current flow to the separately excitated field winding of said second motor-generator when the field excitation current to said second motor-generator has reached its maximum value in either direction.

8. In a driving mechanism the combination as claimed in claim 6, wherein the gear ratio between each successive 18 gear step of said gear box is equal to the ratio between the maximum and minimum speed of said output shaft obtainable by changing the field excitation of said second motor generator from its maximum value in one direction to its maximum value in opposite direction. j

9. In a driving mechanism the combination as claimed in claim 6, wherein said control means for adjusting and reversing the separately excitated field of said second motor-generator includes an annular electrical resistance having twospaced terminals connected to a sourceof direct current and two spaced terminals connected to points of the respective branches of said resistance having a middle potential relatively said firstmentioned terminals, said latter terminals being connected to one end of the separately excitated field Winding of said second motor-generator, and a rotatable contact arm connected to the other end of said field winding and serving as a trolley arm capable of progressively contacting points of said annular resistance having different potential when sweeping thereover. j

10. In a driving mechanism the combination of a driving unit having a certain maximum power, a "driving shaft driven by said driving unit, accelerator means for said driving unit for increasing the speed of said driving unit and hence of said driving shaft-froma lower starting speed to a working speed considerably higher than said starting speed means for maximizing the said working speed of said driving shaft at a preselected value, a planetary gear unit including a ring gear, a sun gear and a planet gear carrier having planet gears each in mesh with both said ring gear and said sun gear, one of said elements of said planetary gear unit being coupled to said driving shaft of said driving unit, an output shaft of the mechanism coupled to a second one of said elements of said planetary gear unit, a first directcurrent motor-generator coupled to the third one of said elements of said planetary gear unit, said first motorgenerator having a maximum power considerably lower than the power of said driving unit, a separate field excitation equipment for said first motor-generator, a second direct-current motor-generator coupled to one of said planetary gear unit elements other than that coupled to said first motor-generator, said second motorgenerator having a maximum power substantially equal to that of said first motor-generator, said two motorgenerators having armatures electrically connected in series, a separate field excitation equipment for said second motor-generator including control means for adjusting and reversing the separately excitated field of said second motor-generator, and means for keeping said control means in a position assuring such a field excitation in said second motor-generator during the operation of said accelerator means of said driving unit that the armature voltage induced in said second motor-generator is lower than but has an opposite polarity to the armature voltage induced in said first motor-generator, so that the said output shaft is caused to accelerate from standstill to a certain working speed as soon as said accelerator means is actuated.

11. In a driving mechanism the combination of a driving unit having a certain maximum power, a driving shaft driven by said driving unit, accelerator means for said driving unit for increasing the speed of said driving unit and hence of said driving shaft from a lower starting speed to a working speed considerably higher than said starting speed, means for maximizing the said working speed of said driving shaft at a preselected value, a planetary gear unit including a ring gear, a sun gear and a planet gear carrier having planet gears each in mesh with both said ring gear and said sun gear, one of said elements of said planetary gear unit being coupled to said driving shaft of said driving unit, an output shaft of the mechanism coupled to a second one of said elements of said planetary gear unit, a first directcurrent motor-generator coupled to the third one of said elements of said planetary gear unit, said first motorgenerator having a maximum power considerably lower than the power of said driving unit, a separate 'field excitation equipment for said first motor-generator a second direct-current motor-generator coupled to one of said planetary gear unit elements other than that coupled to said first motor-generator, said second motorgenerator having a maximum power substantially equal to that of said first motor-generator, said two motorgenerators having armatures electrically connected in series, a separate field excitation equipment for said second motor-generator including control means for adjusting and reversing the separately excitated field of said second motor-generator, means for keeping said control means in a position assuring such a field excitation in said second motor-generator during the operation of said accelerator means of said driving unit that the armature voltage induced in said second motor-generator is lower than but has an opposite polarity to the armature voltage induced in said first motor-generator, so that the said output shaft is caused to acceleratefrom standstill to a certain working speed as soon as said accelerator means is actuated, a step gear box interconnected between said output shaft of the mechanism and that planet gear unit element coupled to said output shaft, the gear ratio between each subsequent gear step of said gear box being equal to the ratio between the maximum and minimum speed'of said output shaft obtainable by actuation of said control means changing the field excitation of said second motor-generator from its maximum value inone direction to its maximum value in opposite direction, a clutch between said gear box and said last mentioned planetary gear unit element, and means responsive to said control means for operating said clutch and for shifting gear in said gear box, upon each full stroke of said control means.

References Cited in the file of this patent UNITED STATES PATENTS 1,515,322 Ahlm Nov. 11, 1924 2,000,465 Higley May 7, 1935 2,018,336 Weichsel Oct. 22, 1935 2,588,750 Nims et a1. Mar. 11, 1952 FOREIGN PATENTS 500,853 France Q Mar. 26, 1920 919,988 France Dec. 16, 1946 760,370 Germany May 11, 1953 669,530 Great Britain Apr. 2, 1952 

